Modern motor vehicles are often equipped with at least one airbag in order to protect those travelling in the vehicle. In a known manner, this airbag is arranged to, in case of a collision with the vehicle, be activated by means of an acceleration sensor and to be inflated by means of a gas generator, so that gas flows into the airbag which is then formed to a soft cushion which suppresses the forward motion of the person travelling in the vehicle. As regards the driver of the vehicle, he is normally protected by means of an airbag which is arranged in the hub of the steering wheel of the vehicle. For this purpose, an airbag module which comprises the airbag and the gas generator used for inflating the airbag can be arranged in the hub of the steering wheel.
When the engine idles the steering wheel normally vibrates at a certain frequency, which frequency is ca. 30-40 Hz in modern vehicles. If an airbag module of the above-mentioned kind is arranged in the steering wheel, a considerable weight is added, which might cause the natural frequency of the steering system of the vehicle to decrease. In case of unfavourable circumstances which i.a. depend on the choice of idling rpm of the engine, the natural frequency can interact with the idling frequency of the engine, thus causing greatly amplified vibrations in the steering wheel.
These amplified vibrations are naturally perceived as something negative by those travelling in the vehicle, in particular by the driver of the vehicle since he is holding the wheel.
There is thus a need for an improved suspension of an airbag module arranged in the steering wheel of a vehicle which enables the vibrations in the steering system and the wheel to decrease. In particular, it is desirable to ensure that the frequency of resonance for the airbag module does not coincide with the vibration frequency at the idling rpm of the vehicle.
The airbag module is furthermore arranged to activate an airbag in a predetermined manner. In particular, it is necessary for the airbag, when triggered, to be inflated in a well defined direction relative to the person intended to be protected. A drawback of known suspension devices for airbag modules is that there is a risk that the airbag is inflated somewhat obliquely, e.g. in the wrong direction relative to the person. As a result, the airbag will not have the intended protective effect. For this reason, there is a need for devices which provide a correct guidance of the airbag when inflating.
A previously known device which relates to a suspension device for an airbag module is shown in patent document U.S. Pat. No. 5,024,464. This device comprises an airbag module which is arranged at a steering wheel via an elastic organ. The airbag module then functions as a vibration attenuator which causes a reduction of the vibrations in the steering wheel. The elastic organ comprises a stop element in the shape of a stud, around which an elastic casing-like element is arranged. The stop element prevents the airbag module from moving upwards more than a certain distance.